From http://www.mayoclinic.com/health/hoarding/DS00966:
Hoarding is the excessive collection of items that seem to have limited or no value, such as newspapers or trash, along with the inability to discard them. Hoarding creates such cramped living conditions that entire rooms may be filled to capacity, and homes may be left with only narrow pathways winding through stacks of clutter. Some people also collect animals, keeping hundreds of dogs, cats or other animals in their homes, as filth and waste pile up and the animals become sick.